Isomaltose is a rare saccharide that merely exists in nature in fermented foods in a slight amount, and it is known to be produced by conventional methods such as partial hydrolysis reactions using acid catalysts, enzymatic reactions using dextranase or isomaltodextranase, reverse-synthetic reactions for forming isomaltose from glucose using glucoamylase or acid catalysts, and glucose-transferring reactions for forming isomaltose from maltose or maltodextrins using α-glucosidase. However, the above conventional methods are far from a satisfactory industrial-scale production of isomaltose, because the isomaltose contents in the reaction mixtures, obtained by the above conventional processes, are only about 10 to about 25% (w/w) (the symbol “% (w/w)” is abbreviated as “%” throughout the specification, unless specified otherwise), on a dry solid basis (d.s.b.) and their purities are relatively low. To improve this drawback, for example, a column chromatography, disclosed in Japanese Patent Kokai No. 72,598/83, can be mentioned. According to the method, a relatively high purity isomaltose can be produced from material saccharide solutions with an isomaltose content of about 10 to about 25%, d.s.b. However, even if the method is employed, there still remains a problem of that the purity and the yield of the produced isomaltose inevitably depend on the isomaltose content in the material saccharide solutions used.
Under these circumstances, there has been required a novel process for producing isomaltose on an industrially scale and in a lesser cost and a higher yield.
While isomaltitol is a sugar alcohol having satisfactory non-reducibility, low sweetness, and moisture-retaining ability, and it is a useful sugar alcohol which has been extensively used in food products, cosmetics, pharmaceuticals, etc., in the form of a saccharide mixture with sorbitol, maltitol, and glucosyl-1,6-mannitol.
Isomaltitol can be theoretically prepared by hydrogenating, i.e., reducing the reducing group of paratinose or isomaltose, as a reducing oligosaccharide, into an alcohol group. In particular, although isomaltitol has been prepared from isomaltose in a relatively high yield, the desired industrial supply of material isomaltose has not been satisfactory. Isomaltose is known to be prepared by the methods such as partial hydrolytic reactions of dextrans using acid catalysts, enzymatic reactions using dextranase or isomaltodextranase, reverse-synthetic reaction for forming isomaltose from glucose using glucoamylase or acid catalysts, glucose-transferring reactions for forming isomaltose from maltose or maltodextrins using α-glucosidase. However, the above conventional methods are far from a satisfactory industrial-scale production of isomaltitol, because the isomaltose contents in the reaction mixtures, obtained by the above conventional processes, are only about 10 to about 25%, d.s.b., and the purity of isomaltitol, obtained by hydrogenating the above-identified isomaltose, is relatively low. To improve the drawback, for example, by applying column chromatography disclosed in Japanese Patent Kokai No. 72,598/83, a relatively high purity isomaltose can be obtained from material saccharide solutions with a relatively low isomaltose content of about 10% to about 25%, d.s.b., and then hydrogenated to obtain isomaltitol. Even in the process for producing isomaltitol, as a drawback, the yield and the cost of isomaltitol inevitably depend on the isomaltose content of the material saccharide solutions used, and this lowers the yield and increases the production cost of isomaltitol.
While in the case of producing isomaltitol from paratinose, the material paratinose is known to be prepared, for example, from sucrose through glucose-transferring reaction using α-glucosyl transferase. However, since the resulting reaction mixture comprises, as by products, trehalulose as an isomer of paratinose and others such as glucose and fructose as hydrolyzates of paratinose, the paratinose content in the reaction mixture could not be over about 85%, d.s.b. In producing isomaltitol from paratinose, glucosyl-1,6-mannitol is formed along with isomaltitol in a production ratio of, usually, 1:1 by weight, and this lowers the purity and the yield of isomaltitol as a drawback.
Under these circumstances, a novel process for producing isomaltitol on an industrial scale and in a lesser cost and a higher yield has been strongly required.